1. Field of the Invention
This invention relates to an automatic exposure control apparatus, and more particularly to an automatic exposure control apparatus for use in a camera in which exposure is controlled on the basis of three-parameters, for example diaphragm aperture, shutter speed and filter transmittance, and in which proper exposure can automatically be determined by preselecting the settings for any two of three parameters and by then automatically determining the setting for the remaining parameter in accordance with the preselected settings for the two preselected parameters.
2. Description of the Prior Art
In the system commonly used in conventional cameras with a built-in automatic exposure control apparatus, either the diaphragm aperture setting or the shutter speed setting is preselected while the remaining setting is automatically determined thereafter in accordance with the preselected settings and in consideration of prevailing light conditions. There is also known a programmed-type camera which permits exposure control to be accomplished by automatic setting of both the diaphragm aperture and the shutter speed at one time. In the two types of cameras mentioned above, two exposure control parameters, ordinarily diaphragm aperture and shutter speed, are employed for controlling exposure. In controlling the exposure in accordance with these cameras, the speed of the film loaded in the camera is also a factor which determines the proper exposure. In taking pictures, however, the diaphragm aperture setting plays a very important role not only in adjusting the exposure to the scene brightness but also in determining the focal depth, and the sutter speed setting is a predominant determining factor in blurring of the photographed image. Therefore, the settings for these two exposure parameters should preferably be preselected according to the aims of the photographer so that he may obtain the desired depth of field and degree of clarity (or blur) in the photographed image. In accordance with the conventional automatic exposure control cameras mentioned above, the setting for one or the other of the two parameters is preselected and the setting for the other parameter is determined solely on the basis of the setting for the preselected parameter. However, such a system does not give the photographer the desired freedom in selection of conditions and therefore presents a problem regarding convenience of operation.
In order to overcome this problem, the so-called three-parameter controlled exposure camera has been developed. In this type of camera, the settings for two parameters, for example, diaphragm aperture and shutter speed, are first preselected according to the aims of the photographer, and the exposure is then adjusted by setting the transmittance of a variable filter in accordance with the preselected settings of the first two parameters. In operating the above camera, it may also happen that when an object is to be photographed under certain ambient light conditions or a certain speed of film is to be used, the amount of light through the variable filter should preferably first be set and one or the other of the shutter speed and diaphragm aperture should be set thereafter in consideration of the light conditions or the film speed. This type of camera should desirably be so arranged that it permits any two of the three parameters to be preselected.